Technical Field
This invention relates to the art of making rhodium-alumina catalysts useful in the conversion of nitrogen oxides contained within the exhaust stream of an internal combustion engine, and more particularly to the use of amino polymers for enhancing the conversion efficiency of catalyst metals.
Discussion of the Prior Art
Rhodium-containing inorganic compounds (i.e., rhodium nitrate, [(Rh(NO.sub.3).sub.3 ], rhodium chloride RhCl.sub.3, and amino rhodium complexes) have been used in the making of reduction catalysts for some time (see Japanese patents 84-184674/30 and 75180A/42; U.S. Pat. Nos. 4,172,047 and 4,020,013). Amino polymers have been used with catalyst metals to obtain increased conversion efficiency for certain chemical reactions. Such catalyst metal-amino polymers have been permanently bonded to the catalyst metal and thus limited to low temperature catalytic applications because such polymers decompose at higher temperatures. Such bonded polymers are not suitable for automotive applications which demand high temperature performance (see U.S. Pat. Nos. 4,098,727; 4,179,402; 4,179,403; 4,306,085; and 4,526,884).
It would be desirable to obtain enhanced level of reduction efficiency for nitrogen oxides by a catalyst prepared with the economy of rhodium chloride or nitrate compounds and without the need for permanent bonding of amino polymers.